Portable Detection Apparatus and Method

ABSTRACT

A portable detection apparatus can include a housing, a first detector for detecting ionizing radiation from a first subject and a second detector within the housing for the detecting the background radiation. A shield within the housing can surround the first and second detectors and define a shield aperture around the first and second detectors for radiation from the subject to enter the housing. A radiation blocking member can substantially block at least a portion of the ionizing radiation from reaching the second detector, whereby radiation detected by the second detector comprises substantially only the background radiation. A processor module can be connected to the first and second detectors for determining the amount of ionizing radiation detected by the first detector attributable to secondary radiation.

RELATED APPLICATIONS

This application claims the benefit of 35 USC 119 based on the priorityof U.S. Provisional Patent Application 61/552,199, filed Oct. 27, 2011and international patent application PCT/CA2012/050764, filed Oct. 26,2012, both applications being incorporated herein in their entirety byreference.

FIELD

The present subject matter relates generally to a portable radiationdetection apparatus and method.

INTRODUCTION

US Patent Pub. No. 2011/0192981 relates to a radiation detection systemthat can include a scintillating member including a polymer matrix, afirst scintillating material and a second scintillating materialdifferent from the first scintillating material and at least onephotosensor coupled to the scintillating member. The radiation detectionsystem can be configured to receive particular radiation at thescintillating member, generate a first light from the firstscintillating material and a second light from the second scintillatingmaterial in response to receiving the particular radiation, receive thefirst and second lights at the at least one photosensor, generate asignal at the photosensor, and determine a total effective energy of theparticular radiation based at least in part on the signal. Practicalapplications of the radiation detection system can include identifying aparticular isotope present within an object, identifying a particulartype of radiation emitted by the object, or locating a source ofradiation within the object.

WO 2011/0877861 relates to a gamma-neutron detector based on mixtures ofthermal neutron absorbers that produce heavy-particle emission followingthermal capture. The detector consists of one or more thin screensembedded in transparent hydrogenous light guides, which also serve as aneutron moderator. The emitted particles interact with the scintillatorscreen and produce a high light output, which is collected by the lightguides into a photomultiplier tube and produces a signal from which theneutrons are counted. Simultaneous gamma-ray detection is provided byreplacing the light guide material with a plastic scintillator. Theplastic scintillator serves as the gamma-ray detector, moderator andlight guide. The neutrons and gamma-ray events are separated employingPulse-Shape Discrimination (PSD). The detector can be used in severalscanning configurations including portal, drive-through, drive-by,handheld and backpack, etc.

SUMMARY

This summary is intended to introduce the reader to the more detaileddescription that follows and not to limit or define any claimed or asyet unclaimed invention. One or more inventions may reside in anycombination or sub-combination of the elements or process stepsdisclosed in any part of this document including its claims and figures.

Following a radiological/nuclear (RN) emergency, such as release ofradioactive substances in nuclear accidents at power plants or localcontamination incidents involving in misuse of radioactive sources, andillicit dispersion of radioactivity in a radiological dispersal device(RDD) by terrorists, the population may be internally exposed toradionuclides. It may be desirable to provide on-site testing to screensubjects that have been exposed to radionuclides to determine whichsubjects may require further medical care.

Radiological emergency sites may also include high levels of backgroundradiation. The presence of background radiation may make it difficult toaccurately determine a subject's individual radiation exposure. It maybe desirable to provide a detection apparatus that is portable (forexample so that it can be transported to the site of a radiologicalemergency) and that is configured to measure a subject's radiationexposure. The detection apparatus may optionally be configured to helpdistinguish radiation being emitted from a subject from the surroundingbackground radiation.

According to one broad aspect of the invention, a portable detectionapparatus can include a housing and a first detector within the housingfor detecting ionizing radiation comprising background radiation andsecondary radiation from a subject. The detection apparatus can alsoinclude a second detector within the housing for the detecting thebackground radiation. A shield can be provided within the housing tosurround the first and second detectors and define a shield aperturearound the first and second detectors for radiation from the subject toenter the housing. The detection apparatus can also include a radiationblocking member substantially blocking at least a portion of theionizing radiation entering the housing through the shield aperture fromreaching the second detector. Radiation detected by the second detectorcan include substantially only the background radiation. The detectionapparatus can also include a processor module connected to the first andsecond detectors for determining the amount of ionizing radiationdetected by the first detector attributable to the secondary radiation.

The housing can define a detection apparatus axis and can be axiallyalignable with the subject. The first detector can include a firstscintillator having an exposed first detection surface extending in agenerally lateral direction and positionable opposite the subject. Thesecond detector can include a second scintillator having a seconddetection surface extending in the generally lateral direction.

The radiation blocking member can cover substantially all of the seconddetection face. The secondary radiation can be substantially preventedfrom reaching the second detection face.

The shield apparatus can laterally surround the first scintillator andthe second scintillator. The shield aperture can be registered with thefirst detection surface and the second detection surface.

The first scintillator can produce a first light when excited by theionizing radiation and the second scintillator can produce a secondlight when excited by the ionizing radiation. The detection apparatuscan also include a photosensor positioned adjacent the first and secondscintillators to receive the first light and generate a correspondingfirst output signal, and to receive the second light and generate acorresponding second output signal.

The processor module an be operably linked to the photosensor and can beoperable to determine the amount of ionizing radiation detected by thefirst detector attributable to the secondary radiation by comparing thesecond output signal with the first output signal.

The processor module can be operable to determine a quantity of theradioactive material contained in the subject based on the amount ofionizing radiation detected by the first detector attributable to thesecondary radiation measured by the detection apparatus.

The processor module can be operable to compare at least one of theamount of ionizing radiation detected by the first detector attributableto the secondary radiation and the quantity of radioactive materialcontained in the subject to a predetermined alarm threshold value andgenerate an alarm signal if the at least one of the amount of ionizingradiation detected by the first detector attributable to the secondaryradiation and the quantity of radioactive material contained in thesubject exceeds the alarm threshold value.

The photosensor can include a first photomultiplier tube to receive thefirst light and generate the first output signal and a secondphotomultiplier tube to receive the second light and generate the secondoutput signal.

The radiation blocking member can have a thickness between about 0.05 mmand about 5 mm.

The radiation blocking member can include a plate member.

The plate member can include at least one of copper, tin, and aluminumor a combination thereof.

The radiation blocking member may allow transmission of the backgroundradiation there through, whereby the background radiation can reach thesecond detector.

The shield can include a first shielding layer formed from a firstmaterial, a second shielding layer formed from a second material anddisposed laterally inboard of the first shielding layer, and a thirdshielding layer disposed laterally inboard of the second shieldinglayer.

The first shielding layer can have a first lateral width, the secondshielding layer can have a second lateral width and the third shieldinglayer can have a third lateral width. The first lateral width can begreater than the both the second and third lateral widths.

The first shielding layer can be formed from lead or tungsten, and thefirst lateral width can be between about 2.5 mm and 125 mm.

The second shielding layer can be formed from tin, and the secondlateral width can be between about 0.25 mm and about 25 mm.

The third shielding layer can be formed from copper, and the thirdlateral width can be between about 0.25 mm and about 25 mm.

The first and second scintillators can include first and seconddetection crystals, respectively.

The first scintillator can have an overall surface area and the firstdetection surface can have a detection surface area. The detectionsurface area can be between about 25% and about 45% of the overallsurface area.

The first scintillator can have a first thickness in the axial directionof less than about 25 mm.

The first and second detection crystals can include NaI(TI) crystals.

The second scintillator can be generally identical to the firstscintillator.

The time elapsed between exposure of the detection apparatus to thesource of the secondary radiation and obtaining the resultant outputsignal defines a detection cycle time, and the detection cycle time canbe less than about 10 minutes.

The detection cycle time can be less than about 2 minutes.

The detection apparatus can be a mountable on a vehicle.

Radioactive material within the subject can emit beta radiation and thesecondary radiation can be bremsstrahlung radiation produced by aninteraction between the beta radiation from the radioactive material andthe subject.

The detection apparatus can be configured to measure photons having anenergy that is less than about 500 keV.

The detection apparatus can be configured to measure photons having anenergy that is greater than about 30 keV.

The detection apparatus can have an operating sensitivity capable ofdetecting an activity of at least about 460 Bq within the subject usinga 5 minute scan.

According to another broad aspect of the invention, a portable radiationdetection system can include a vehicle and a portable radiationdetection apparatus mounted on and transportable with the vehicle.

The vehicle can include a radiation shielded chamber, and the first andsecond detectors can be provided within the shielded chamber.

According to yet another broad aspect of the invention, a method ofmeasuring the quantity of a beta-emitting radioactive material within asubject using a portable detection apparatus can include the steps of a)positioning the portable detection apparatus adjacent the subject. Theportable detection apparatus can include a first detector, configured todetect ionizing radiation comprising background radiation and secondaryradiation, and a second detector configured to detect ionizingradiation. The method can also include the steps of b) detecting acombination of the secondary radiation and the background radiationusing the first detector and providing a corresponding a first outputsignal, c) simultaneously detecting the background radiation using thesecond detector and providing a corresponding second output signal; andd) automatically calculating a resultant output value based on at leastthe first output signal and the second output signal.

The method can include the step of comparing the resultant output valueto a predetermined alarm threshold value, and generating an alarm outputif the resultant output value exceeds the alarm threshold value.

Calculating the resultant output value can include comparing subtractingthe second output signal from the first output signal to determine afirst quantity of secondary radiation received by the detectionapparatus.

Calculating the resultant output value can also include determining asecond quantity of radioactive material contained within the subjectbased on the first quantity of secondary radiation.

The resultant output value can include at least one of the firstquantity of secondary radiation and the second quantity of radioactivematerial.

The method can also include transporting the portable detectionapparatus to a temporary testing location.

The method can also include positioning a radiation blocking memberbetween the second detector and the subject to inhibit the secondaryradiation from reaching the second detector.

DRAWINGS

The drawings included herewith are for illustrating various examples ofarticles, methods, and apparatuses of the teaching of the presentspecification and are not intended to limit the scope of what is taughtin any way.

In the drawings:

FIG. 1 is a perspective view of a portable detection apparatus;

FIG. 2 is an end view of the portable detection apparatus of FIG.

FIG. 3 is a perspective view of a first scintillator useable with thedetection apparatus of FIG. 1;

FIG. 4 is a section view taken along line 4-4 in FIG. 2;

FIG. 5 is a perspective view of the portable detection apparatus of FIG.1 positioned adjacent a patient;

FIG. 6 is an enlarged view of area 6 as shown on FIG. 5, with a portionof the detection apparatus housing cut-away;

FIG. 7 is a schematic representation of a processor module useable withthe detection apparatus of FIG. 1;

FIG. 8 a is a perspective view of another example of a detectionapparatus;

FIG. 8 b is a perspective view of yet another example of a detectionapparatus;

FIG. 9 is a partial cut-away view of a portable radiation detectionsystem;

FIG. 10 is a flow chart illustrating a method of using a portabledetection apparatus;

FIG. 11 is a graph illustrating detector response for a variety ofradioactive compounds;

FIG. 12 is a graph illustrating a comparison between combined backgroundand secondary radiation signals and background radiation signals for anunshielded detection apparatus;

FIG. 13 is a graph illustrating a comparison between combined backgroundand secondary radiation signals and background radiation signals for ashielded detection apparatus;

FIG. 14 is a graph illustrating detector efficiency as a function ofscintillator thickness; and

FIG. 15 is a graph illustrating photomultiplier tube signal variationfor different thickness of the aluminum scintillator housing.

Elements shown in the figures have not necessarily been drawn to scale.Further, where considered appropriate, reference numerals may berepeated among the figures to indicate corresponding or analogouselements.

DETAILED DESCRIPTION

Various apparatuses or processes will be described below to provide anexample of an embodiment of each claimed invention. No embodimentdescribed below limits any claimed invention and any claimed inventionmay cover processes or apparatuses that differ from those describedbelow. The claimed inventions are not limited to apparatuses orprocesses having all of the features of any one apparatus or processdescribed below or to features common to multiple or all of theapparatuses described below. It is possible that an apparatus or processdescribed below is not an embodiment of any claimed invention. Anyinvention disclosed in an apparatus or process described below that isnot claimed in this document may be the subject matter of anotherprotective instrument, for example, a continuing patent application, andthe applicants, inventors or owners do not intend to abandon, disclaimor dedicate to the public any such invention by its disclosure in thisdocument.

Following a radiological/nuclear (RN) emergency, such as release ofradioactive substances in nuclear accidents at power plants or localcontamination incidents involving in misuse of radioactive sources, andillicit dispersion of radioactivity in a radiological dispersal device(RDD) by terrorists, the population may be internally exposed toradionuclides. Rapid bioassay can be important to identify thecontaminated individuals and to provide quick dose information to thephysicians for necessary medical treatment. As a bone-seeking elementand a pure beta emitter with notable commercial uses, Strontium-90(⁹⁰Sr) has been identified as one of the high-risk radionuclides or RDDsby the U.S. Department of Energy (DOE) and the U.S. Nuclear RegulatoryCommission (NRC) interagency working group (the U.S. DOE/NRC 2003).

⁹⁰Sr is a radioactive isotope of strontium, with a half-life ofapproximately 28 years and a maximum beta energy of 0.546 MeVdistributed to an electron, an anti-neutrino and the yttrium isotope ⁹⁰Y(with a half-life of 64 hours and a maximum beta energy of 2.228 MeV).⁹⁰Sr/Y is almost a pure beta source, and gamma emissions from the decayof ⁹⁰Sr/Y can be very weak.

Compared to substances that are strong gamma emitters, it may berelatively easier to shield the beta particles emitted by ⁹⁰Sr/Y (orother substantially pure high-energy beta-emitting sources, including,for example Phosphorous-32) from conventional detection techniques, forexample by using shielding packing structures and materials. Betasources are also more difficult to detect than gamma sources. Thus, aRDD using ⁹⁰Sr source is more attractive to the terrorists as it wouldbe easy to carry and difficult to monitor while in delivery to thetarget location. In an emergency involving internal contamination of⁹⁰Sr, large populations may need to be screened for early medicalresponse.

For example, if exposed to air-borne ⁹⁰Sr/Y particles, a patient mayinhale a quantity of ⁹⁰Sr/Y, which can then become lodged in thepatient's lungs. The health risk posed to the patient can vary based onthe quantity of ⁹⁰Sr/Y material present in the patient's lungs. To helpfacilitate diagnosis of patients exposed to ⁹⁰Sr/Y in this manner, itmay be desirable to screen each patient to determine his/her exposurelevel.

Traditional ⁹⁰Sr/Y screening apparatuses include large room-sized testchambers (for example within a hospital or other facility) withextensive radiation shielding to filter out substantially all of theambient/background radiation. Background radiation can include radiationemitted from a variety of sources, including, for example, cosmic rays,natural radioactive background of surrounding materials (such asconcrete, etc.).

Conventional radiation shielding can include thick layers of lead (orother suitable materials). A patient is then placed within the testingroom and radiation emitted from the patient is monitored using asuitable detector. This type of screening can produce relativelyaccurate results, but typically takes approximately 20 mins or longer toscreen one patient. In instances of mass exposure to ⁹⁰Sr/Y, traditionalscreening methods may require a relatively long scan time per patient,which may limit the number of patients that can be screened in a giventime period.

Also, transporting a large number of patients to a suitable medicalfacility for screening may take a long time and may not be practical insome situations. Further, transporting patients prior to screening forexposure to ⁹⁰Sr/Y may result in the transport of non-contaminatedpatients. Transporting non-contaminated patients to a secondary medicalfacility may be unnecessary and may consume resources that couldotherwise be used to transport and treat contaminated patients.

To help facilitate the screening of patients on-site at a temporarytesting location (i.e. generally at the scene of the ⁹⁰Sr/Y exposure) arelatively rapid and mobile/portable radiation detection apparatus(optionally useable to detect ⁹⁰Sr/Y and/or any other suitableradioactive material) and technique for ⁹⁰Sr/Y bioassay screening may bedesirable. Preferably, the portable detection apparatus can be moved to,and operated effectively within, a ⁹⁰Sr/Y exposure site. In mostinstances, the portable ⁹⁰Sr/Y detection apparatus may operate withoutthe benefit of the comprehensive radiation shielding that is used inconventional, room-based screening systems. In such instances, thepatient, and the ⁹⁰Sr/Y detection apparatus, may not be substantiallyisolated from the surrounding background radiation.

Preferably, the portable ⁹⁰Sr/Y detection apparatus can be configured tobe mounted on a truck, or other suitable vehicle, including, for examplean airplane and a boat, and can be transported to a ⁹⁰Sr/Y exposuresite.

Preferably, the portable ⁹⁰Sr/Y detection apparatus can be operable toscreen patients at a faster rate than conventional screening systems.For example, the portable ⁹⁰Sr/Y detection apparatus can be configuredto have a screening time that is less than 20 mins per patient, andoptionally can be less than 10 mins per patient and can be between about1 min and about 2 mins per patient, or less than 1 min per patient.

Optionally, a portable ⁹⁰Sr/Y detection apparatus can be configured todirectly monitor the beta radiation emitted by a ⁹⁰Sr/Y source. However,beta radiation emitted from a ⁹⁰Sr/Y source within a patient's lungs canbe partially or completely blocked by the patient's lung tissue andother body parts. Such blockage of the beta radiation can make directdetection of the beta radiation more difficult.

Alternatively, instead of directly monitoring the primary betaradiation, a portable ⁹⁰Sr/Y detection apparatus can be configured tomonitor a type of secondary radiation, which can then be correlated toan amount of beta radiation, and a related quantity of ⁹⁰Sr/Y material,present in the patient's lungs. One example of a measurable, secondaryradiation is bremsstrahlung radiation. Bremsstrahlung radiation (x-rays)is a type of secondary radiation that is produced as a result of thestopping or slowing of the primary radiation (in this case electronsgenerated by the ⁹⁰Sr/Y beta radiation). The amount of bremsstrahlungradiation emitted can be correlated to the amount of incident betaradiation present. The amount of bremsstrahlung radiation produced canbe dependent on the density of the material impacted with betaradiation, and can rise generally with electron energy.

For example, a portable ⁹⁰Sr/Y detection apparatus can be configured todetect bremsstrahlung radiation present emitted by the patient, and todetermine the amount of beta radiation and/or ⁹⁰Sr/Y material presentbased at least in part on the quantity of bremsstrahlung radiationdetected.

Optionally, the portable ⁹⁰Sr/Y detection apparatus can also beconfigured to account for, and optionally filter out backgroundradiation. Filtering out background radiation may help facilitate a moreaccurate reading of the secondary bremsstrahlung radiation levelspresent in the patient. For example, the detection apparatus can includea first detector that is configured to detect a combination of secondaryradiation and background radiation, and a second detector that isconfigured to simultaneously detect substantially only the backgroundradiation. The amount of secondary target radiation detected can then becalculated by subtracting the second detector readings from the firstdetector readings.

A radiation blocking member can be used to prevent the secondaryradiation from reaching the second detector. The blocking member can beany suitable material, and can be selected so that it is thick enough(for a given material) to block substantially all the secondarybremsstrahlung radiation. The background radiation can be higher energythan the secondary radiation, and can pass through the blocking memberto reach the second detector. Background radiation can come from allsides of the detection system (including, for example, naturalradioactivity produced by common materials—K, U, Th). In contrast, thesecondary bremsstrahlung radiation is emitted from the subject.Positioning the blocking member between the second detector and thesubject may help prevent the secondary radiation from reaching thesecond detector.

In addition to detecting ⁹⁰Sr/Y, the teachings disclosed herein may alsobe useful for detecting other pure beta emitters, including, forexample, P-32, Sr-89, Dy-165, Bi-210, Pd-109, Pr-143, Ho-166 and Pm-149.Some of all of these isotopes may have potential for use in nuclearmedicine diagnostics and/or treatments. Measuring the relativeconcentrations of these materials according to the teachings disclosedherein may be advantageous, and may allow for more precise measurement,and/or measurement of relatively smaller quantities of such isotopesthan is currently practical using known measurement techniques and/orapparatuses. The teachings disclosed herein may also reduce the timerequired to obtain a desired measurement, and may allow for portable oron-site measurements of suitable pure, or substantially pure betaemitters.

In addition to detecting/measuring substantially pure beta emitters, theinventor believe that the teachings described herein may also beutilized to detect low energy gamma emitters, including, for example,Am-241, Ce-144, Ce-141 and U-235. For example, the use of a shielded,thin Nal detector (as explained in greater detail below) may allow fordetection of low energy gamma emitters that might otherwise be obscuredby background radiation using known, portable detectors. While thefollowing example of a detection apparatus is illustrated with referenceto detecting ⁹⁰Sr/Y for clarity, optionally the detection apparatus mayalso be configured for use with any other suitable material, including,for example, the isotopes set out above.

Referring to FIG. 1, a portable ⁹⁰Sr/Y detection apparatus 100 includesa housing 102, a first detector 104 within the housing 102 for detectingionizing radiation and a second detector 106 within the housing 102 fordetecting ionizing radiation. The detection apparatus 100 also includesa radiation shield 108 (shown in dashed lines, see also FIG. 4), aradiation blocking member 110 and a processor module 112 (FIG. 4)connected to the first and second detectors 104, 106. The first andsecond detectors 104, 106 can be used simultaneously to measure theionizing radiation. The blocking member 110 can be used to block atleast a portion of the ionizing radiation from reaching the seconddetector 106, so that the radiation readings from the first and seconddetectors 104, 106 are different. The readings from the first and seconddetectors 104, 106 can then be compared by the processor module 112 toarrive at a resultant reading (for example the difference between thefirst detector reading and the second detector reading). The resultantreading can be provided to a system operator, and/or used to generate analarm, a resultant output signal or other output.

The detection apparatus 100 has a first end 114 (suitable forpositioning adjacent a subject) and a second end 116 spaced apart fromthe first end. The detection apparatus defines a longitudinal axis 118extending between the first and second ends.

The ionizing radiation detected by the first and second detectors 104,106 can be any suitable type of secondary radiation (compatible with thedetectors selected) and can include a combination of backgroundradiation and secondary radiation from the subject. The secondaryradiation can be any radiation, generally emitted from the subject thata system operator wishes to measure. The background radiation caninclude radiation from a variety of sources, and can include radiationemitted from sources other than the subject. The processor module 112 isoperable to determine the amount of ionizing radiation detected by thefirst detector that is attributable to secondary radiation, as opposedto the background radiation.

In some instances, the background radiation and secondary radiation maybe similar forms of radiation, including, for example beta radiation,Bremsstrahlung radiation and x-ray radiation, and may have similarenergy levels. Preferably, both the first and second detectors 104, 106are capable of detecting the background radiation, and at least one ofthe detectors, for example the first detector 104, is also capable ofdetecting the secondary radiation.

Referring To FIGS. 5 and 6, in the example illustrated, the subject is ahuman patient 120 that has been exposed to ⁹⁰Sr/Y, and the detectionapparatus 100 can be positioned adjacent the torso of the patient 120.Optionally, the detection apparatus can be positioned generally adjacentthe lungs 122 of the patient 120. This configuration may help facilitatedetection of ⁹⁰Sr/Y radioactive material 124 (schematically representedas a single particle 124) that has been inhaled by the patient 120, andhas become lodged in the patient's lungs 122. In this example, the decayof ⁹⁰Sr/Y radioactive material 124 within the patient's lungs 122 mayrelease ionizing beta radiation 126 (schematically represented as soliddots 126). This beta radiation 126 may interact with the bones, organsand tissue of the patient's torso and may produce Bremsstrahlungradiation 128 (schematically represented as hollow dots 128). TheBremsstrahlung radiation 128 can then form at least a portion of thesecondary radiation emitted from the patient's torso, and can bemeasured using the detection apparatus 100.

Referring to FIGS. 3 and 4, the first detector 104 includes a firstscintillator 130 a having a first detection face 132 a extendinggenerally in the lateral direction (i.e. generally orthogonal to thelongitudinal axis), and a first rear face 134 a axially spaced apartfrom the first detection face 132 a. A first sidewall 136 a extendsbetween the first detection face 132 a and the first rear face 134 a.

The second detector 106 includes a second scintillator 130 b having asecond detection face 132 b extending generally in the lateraldirection, and a second rear face 134 b axially spaced apart from thesecond detection face 132 b. A second sidewall 136 b extends between thesecond detection face 132 b and the second rear face 134 b. When thedetection apparatus 100 is in use, the first detection surface 132 a andsecond detection surface 132 b can be positioned facing the torso of thepatient 120, and optionally can be placed in physical contact againstthe front or back of the torso of the patient 120.

In the illustrated example, both the first and second detectors 104, 106are generally cylindrical in shape, and the first and second detectionfaces 132 a, 132 b are generally circular in cross-section. Thescintillators 130 a, 130 b have respective diameters 138 and lengths140. In the example illustrated, the scintillator diameters 138 a, 138 bcan be between about 25 mm and about 125 mm, and between about 50 mm andabout 100 mm, and can be approximately 75 mm. Optionally, thescintillator diameters 138 a, 138 b can be less than about 25 mm orgreater than about 125 mm.

The scintillator lengths 140 a, 140 b can be between about 2.5 mm andabout 75 mm, and can be between about 6.5 mm and about 20 mm, andoptionally can be about 12 mm. Optionally, the scintillator lengths 140a, 140 b can be less than 2.5 mm and greater than about 75 mm.

Optionally, the dimensions of the first and second detectors 104, 106can be selected so that the surface area of the detection faces 132 a,132 b is between about 25% and about 45% of the total surface area ofthe first and second detectors 104, 106, respectively (e.g. the sum ofthe surface area of the first detection surface 132 a, the first rearsurface 134 a and the first sidewall 136 a).

The first and second detectors 104, 106 extend along respective detectoraxes 140 a, 140 b. The detector axes 140 a, 140 b can be generallyparallel to the axis 118. The first and second detectors 104, 106 arelaterally separated from each other by a detector spacing distance 142(FIG. 4). The detector spacing distance 142 can be selected such that itis less than 1.5 times the lateral width, in this case the diameter 132a, of the first detector 104. Positioning the first and second detectors104, 106 laterally close to each other may help increase the likelihoodthat the first and second detectors 104, 106 are exposed tosubstantially the same ionizing radiation background. Alternatively, thedetector spacing 142 can be greater than the 1.5 times first diameter132 a.

In the illustrated example, the first and second detectors 104, 106 canbe generally identical. Alternatively, the first and second detectorscan be different.

The scintillators used to provide the first and second detectors 130 a,130 b can be any suitable radiation detecting material. In theillustrated example, the first and second scintillators are sodiumiodide crystals doped with thallium (NaI(TI) crystals). The first andsecond scintillators 130 a, 130 b can each be formed from a singleNaI(TI) crystal, or a plurality of crystals. Alternatively, the firstand second scintillators 130 a, 130 b can be formed from another type ofscintillator material, including, for example, organic crystals, organicliquids, plastic scintillators and inorganic crystals (including alkalimetal halides, lanthanum halides, bismuth germanate and cadmium zinctelluride).

Alternatively, the first and second detectors 104, 106 can be anysuitable type of detector or sensor, that can detect the secondaryradiation, and need not be scintillators having the configurationdescribed herein.

Referring to FIG. 4, the radiation shield 108 is disposed within thehousing 102 and surrounds the first and second detectors 104, 106. Theradiation shield 108 can be any type of apparatus, and/or can be formedfrom any suitable material, that can at least partially shield the firstand second detectors from incoming background radiation.

In the illustrated example, the shield 108 laterally surrounds thesidewalls 136 a, 136 b of the first and second detectors 104, 106, andincludes a shield aperture 144 (see also FIGS. 1 and 2) located towardthe first end 114 of the detection apparatus housing 102.

The shield aperture 144 includes at least one opening in the shield 108to allow radiation to enter the housing 102 and contact the first andsecond detectors 104, 106. Preferably, the shield aperture 144 isprovided in a plane 146 (FIG. 4) that is generally perpendicular to theaxis 118 and is laterally registered with the first and second detectionfaces 132 a, 132 b, so that the first and second 132 a, 132 b are atleast partially overlapped by the aperture 144. This configuration mayallow the first and second detection faces 132 a, 132 b to be exposed toa patient and may help reduce the exposure of the first and seconddetection faces 132 a, 132 b to radiation that is travelling in agenerally non-axial direction.

Referring to FIGS. 5 and 6, when the detection apparatus 100 ispositioned adjacent the torso of a patient 120, and aligned so that thelongitudinal axis 118 intersects the torso of the patient 120, at leasta portion of the secondary radiation 128 emitted from the patient 120may travel through the shield aperture 144 to reach the first and seconddetectors 104, 106, while external background radiation 146 (illustratedby arrows 146) travelling in a non-axial direction may be at leastpartially blocked from reaching the first and second detection surfaces132 a, 132 b.

The shield aperture 144 need not be a single, continuous opening thatoverlaps both the first and second detection surfaces 132 a, 132 b.Optionally, the blocking member 110 can be configured to coversubstantially all of the shield aperture 144 and can include two or morediscrete openings 144 a, 144 b (FIG. 8 a). For example the shieldaperture can include a first opening 144 a registered with the firstdetection face 132 a, and a discrete second opening 144 b registeredwith the second detection surface 132 b. The blocking member 110 can bepositioned to cover the opening 144 b, to help prevent the secondaryradiation from reaching the second detection surface 132 b.Alternatively, referring to FIG. 8 b, the blocking member 110 can beconfigured to cover substantially all of the shield aperture 144, andcan include a single opening 144 a registered with the first detectionsurface 132 a. The second detection face 132 b can be covered by theshield member 110 (as illustrated using dashed lines in FIG. 8 b).

Referring to FIG. 4, in the example illustrated, the shield 108 is amulti-layer apparatus, including a first shielding layer 148 a formedfrom a first material, a second shielding layer 148 b formed from asecond material and disposed laterally inboard of the first shieldinglayer; and a third shielding layer 148 c disposed laterally inboard ofthe second shielding layer. Each shielding layer 148 a-c can be formedfrom any suitable material that can provide a desired degree ofradiation shielding, including, for example, lead, copper, tin,tungsten, aluminium and other suitable materials. Optionally, the shieldlayers 148 a-c can be formed from different materials, or from the samematerial.

The first shielding layer 148 a has a first lateral width 150 a, thesecond shielding layer 148 b has a second lateral width 150 b and thethird shielding layer 148 c has a third lateral width 150 c. Optionally,the first lateral width 148 a can be greater than the both the secondand third lateral widths 148 b, 148 c, and can be greater than the sumof the second and third lateral widths 148 b, 148 c.

In the illustrated example, the first shielding layer 148 a is formedfrom lead, and the first lateral width 150 a can be between about 2.5 mmand 125 mm, or more. The width of the first shield layer 148 a can beselected based on a variety of factors, including, for example, weight,safety and health considerations and radiation shieldingcharacteristics. Reducing the weight of the shield 108 may be desirableand may help increase the portability of the detection apparatus. Insome embodiments, selecting a shield thickness to reduce weight may bemore desirable than achieving a higher level of radiation shielding.

Some radiation shielding materials, effective at blocking certain typesof radiation, can also emit radiation. In some instances, the radiationemitted by the shielding material can be generally similar to thesecondary radiation. In such instances, it may be desirable to configurethe inner shielding layers (for example the second and third shieldinglayers 148 b, 148 c) to help block the radiation emitted by the firstshielding layer 148 a.

For example, lead may be generally effective at blocking gamma and betaradiation, but may emit low levels of x-ray radiation. X-ray radiationemitted by the lead shielding can be generally similar to the secondaryBremsstrahlung radiation 128 emitted by the patient. To help facilitateaccurate target radiation readings, it can be desirable to block thex-ray radiation emitted from the lead shielding from reaching the firstand second detectors 104, 106. In the illustrated example, the secondand third shielding layers 148 b, 148 c are formed from a material otherthan lead, and may help block x-rays emitted by the first shieldinglayer from reaching the detectors. The second and third shielding layers148 b, 148 c can be formed from any suitable material.

In the example illustrated, the second shielding layer 148 b can beformed from tin and the third shielding layer 148 c can be formed fromcopper. The second lateral width 150 b and third lateral width 150 c canbe between about 0.25 mm and about 25 mm, and can be approximately 1 mm.Optionally, the second and third lateral widths can be greater thanabout 25 mm or less than about 0.25 mm.

Referring to FIGS. 2 and 6, the radiation blocking member 110 isconfigured to substantially block at least a portion of the ionizingradiation entering the housing through the shield aperture 144 fromreaching the second detector 106 (shown in phantom in FIG. 2).Preferably, the radiation blocking member 110 is configured so that whenbombarded with ionizing radiation containing a mixture of backgroundradiation 146 and secondary radiation 128, that substantially all of thesecondary radiation 128 is blocked by the blocking member 110, andsubstantially all of the background radiation 146 can pass through theblocking member 110 and reach the second detector 106. In thisconfiguration, the second detector 106 would detect substantially onlythe background radiation.

The blocking member 110 can be formed from any suitable material, havingthe desired radiation shielding properties, and can be any suitablesize.

In the illustrated example, the blocking member 110 includes a platemember coupled to the housing 102 (or optionally integrally formed withthe housing). The radiation blocking member 110 has an axial thickness150 between about 0.25 mm and about 7.5 mm, and can be approximately 2mm thick. Optionally, the blocking member 110 can be formed from copper,tin, aluminium, any other suitable material or a combination thereof. Inthe illustrated example, the blocking member 110 is formed from copper.

Preferably, the blocking member 110 has a surface area that is generallyequal to or greater than the surface area of the second detection face132 b, so that the plate can be positioned to cover all of the seconddetection face 132 b (FIG. 2).

Referring to FIG. 4, the processor module 112 connected to the first andsecond detectors 104, 106 is used to determine the amount of ionizingradiation detected by the first detector 104 attributable to thesecondary radiation 128. Referring also to FIG. 7, the processor module112 can include a central processing unit (CPU) 154, a memory module 156an input module 158 and an output module 160. The processor module 112may also include any other suitable modules. Any of the modules can beprovided as hardware components, firmware components, softwarecomponents and any combination thereof. A power source 162 can also beincluded within the housing 102 to provide power for the processormodule 112 and/or detectors. Optionally, the power source 162 can beprovided within the processor module 112. While illustrated as separatemodules, optionally, some or all of the modules can be integral witheach other.

The input module 158 can by any suitable module adapted to receivesignals 164 from the detectors (optionally, via an intermediateconnecting apparatus as explained below), including, for example, asingle channel or multi-channel data acquisition apparatus,analogue-to-digital convertor, pre-amplifiers, amplifies, FADCs, FPGAs,ASICs, etc.

The output module 160 can be any suitable module adapted to send outputsignals 166 from the processor module 112. The output signals 166 mayinclude any type of signal, including electrical signals, data signals,printed or displayed dosage estimates, visual output signals (such asflashing lights, text on a display screen, etc.), auditory signals (suchas warning sounds or sirens) and control output signals that can be usedto control other pieces of equipment. Examples of suitable outputmodules 160 can include, for example, display screens, lights, audiotransducers and command and control signals. The output module 160 canalso include a transmitter, for example a wireless transmitter 168, fortransmitting output signals 160 from the detection apparatus 100 to anexternal location.

The memory module 156 can be any suitable type of memory that can beread by the CPU 154. The memory module 156 can be configured to storealarm threshold data, look-up tables, databases, apparatus operationalgorithms and any other suitable type of information. The memory can beselectively queried by the CPU 156.

Preferably, the processor module 112 can be contained within the housing102. This configuration may help facilitate transportation of thedetection apparatus 100. A self-contained detection apparatus 100 ofthis type may be more portable than a detection apparatus comprising aplurality of independent pieces. Alternatively, some or all of theprocessor module 112 can be independent from the housing 102 containingthe first and second detectors 104, 106

Referring to FIGS. 4 and 6, in the illustrated example, the firstscintillator 130 a produces a first light when excited by the ionizingradiation and the second scintillator 130 b produces a second light whenexcited by the ionizing radiation. Optionally, a photosensor 170 can bepositioned adjacent the first and second scintillators 130 a, 130 b toreceive the first light and generate a corresponding first outputsignal, and to receive the second light and generate a correspondingsecond output signal. The photosensor 170 can be positioned between thefirst and second detectors 104, 106 and the processor module 112.

In the example illustrated, the photosensor 170 includes a firstphotomultiplier tube 172 a positioned adjacent the first rear face 134 ato receive the first light and generate a corresponding first electricaloutput signal, and a second photomultiplier tube 172 b positionedadjacent the second rear face 134 b to receive the second light andgenerate a corresponding second electrical output signal. The strengthof the first and second output signals can be proportional to the amountof ionizing radiation received by the first and second detectors 104,106, respectively. The photomultiplier tubes (PMTs) 172 a, 172 b can beof any suitable configuration. Outputs from the PMTs 172 a, 172 b aresent to the input module 158 in the processor unit 112.

Alternatively, any other suitable type of connecting apparatus can beused to link the detectors to the processor module. The type ofconnecting apparatus used may depend on the nature of the detectors andprocessor module used. Other examples of connecting apparatuses caninclude amplifiers and analogue-to-digital convertors.

Referring to FIGS. 4 and 6, in the example illustrated the processormodule 112 is operably linked to the photosensor 170 and is operable todetermine the amount of ionizing radiation detected by the firstdetector 104 attributable to the secondary radiation 128 by comparingthe second output signal with the first output signal.

For example, the first output signal from the first PMT 172 a may beproportional to the total amount of background radiation 146 andsecondary radiation 128 received by the first detector 104, and thesecond output signal may be proportional to the total amount ofbackground radiation received by the second detector 106. Due to thepresence of the blocking member 110 that can filter out the secondaryradiation 128, the total amount of radiation received by the seconddetector 106 can be substantially equal to background radiation 146. Theamount the ionizing radiation detected by the first detector 104 that isattributable to the secondary radiation 128 can be determined bysubtracting the second output signal from the first output signal. Theresultant signal is proportional to the amount of secondary radiation128 detected. This operation can be performed by the processor module112.

Optionally, the processor module 112 can be configured to calculate thequantity of secondary radiation 128 emitted from the subject 120, basedon the resultant signal. In the illustrated example, the processormodule 112 may be operable to calculate the amount of Bremsstrahlungradiation 128 emitted from the patient 120, based on the differencebetween the signals from the first and second detectors.

Further, the processor module 112 may also be configured to calculatethe quantity of radioactive material 124 contained within the subject120. In the example illustrated, the processor module 112 may beconfigured to calculate the amount of beta radiation 126 that is presentwithin the patient 120 to produce the measured level of Bremsstrahlungradiation 128, and then calculate the quantity of ⁹⁰Sr/Y 124 presentwithin the subject based on the calculated beta radiation levels.

Optionally, the processor module 112 can be operable to compare at leastone of the amount of ionizing radiation detected by the first detector106 attributable to the secondary radiation (for example the quantity ofBremsstrahlung radiation 128 measured) and the quantity of radioactivematerial contained in the subject (for example the quantity of ⁹⁰Sr/Y124 in the patient) to one or more predetermined alarm threshold valuesstored in the memory module 156. The processor module 112 can thengenerate a warning output signal or an alarm output signal 166 if the atleast one of the amount of ionizing radiation detected by the firstdetector 104 attributable to the secondary radiation 128 and thequantity of radioactive material 124 contained in the subject 120exceeds its corresponding alarm threshold value. The warning and alarmoutput signals can be any suitable output signal, as described above.

When the detection apparatus 100 is in use, the time elapsed betweenexposure of the detection apparatus 100 to the source of the secondaryradiation 128 (e.g. the patient 120) and obtaining the resultant outputsignal can define a detection cycle time. When measuring Bremsstrahlungradiation 128, the precision or resolution of the measurement mayincrease with longer detection cycle time. For example, a conventionalscan performed in a heavily shielded room (for example within ahospital) may produce relatively precise radiation readings, but mayhave a detection cycle time of approximately 20 minutes, or more. Thelength of the scan can be based on the desired accuracy of the results.

However, if the detection apparatus 100 is used as an on-site emergencyscanner, providing relatively precise radiation readings may berelatively less important. Instead, providing a more coarse radiationreading while providing relatively short detection cycle times may beadvantageous, as it may allow multiple patients 120 to be scanned in arelatively short time period. For example, in an emergency bioassay ortriage type situation, it may be sufficient to simply determine if theamount of ⁹⁰Sr/Y a patient has received is above or below a certainthreshold. In such instances, it may not be necessary in the field todetermine precisely how much ⁹⁰Sr/Y a patient has inhaled, but ratherwhether the patient's exposure is high enough to warrant further medicalcare. A more precise scan may then be performed at a hospital or othercare facility if warranted.

When used on-site, the detection apparatus 100 can be configured to havea cycle time that is less than the cycle time of conventional,room-based scanners. Optionally, the detection apparatus 100 can beconfigured to reduce cycle time to help facilitate the relatively rapidscanning of multiple patients, even if such reduced cycle times areachieved by sacrificing the precision of the radiation readings.Configuring the detection apparatus 100 can include modifying theprogramming of the processor module 112 to limit scan times and/or limitthe acquisition threshold or energy spectrum detection range.

Optionally, the detection apparatus can be configured so that thedetection cycle time is less than about 10 minutes, and can about 5minutes and can be less than about 2 minutes.

Optionally, the detection apparatus can be configured to measure photonshaving an energy that is between about 0 keV and about 700 keV, betweenabout 30 keV and about 600 keV and preferably between about 120 keV andabout 500 keV, and filter out energy signals outside of this range.Limiting the energy spectrum detection range may help reduce detectioncycle time.

Optionally, the detection apparatus can be configured to have anoperating sensitivity capable of detecting an activity of at least about460 Bq within the subject using a 5 minute scan. The detection apparatusand method may be a viable technique for detecting ⁹⁰Sr with a minimumdetectable activity (MDA) of 1.1×10⁴ Bq for a realistic dual shieldeddetector system in a 0.25 μGy h⁻¹ background field for a 100 s scan.This MDA is below the action level of 8.2×10⁴ Bq for ⁹⁰Sr intake in thelungs.

Optionally, the detection apparatus 100 can be part of a larger mobileradiation detection system and can be mountable on a vehicle to helpfacilitate transportation of the detection apparatus to a radiologicalemergency site. While an example of a truck is illustrated, thedetection apparatus can be mountable on a variety of vehicles (includingplanes and ships), and/or in a plurality of portable labs or otherstructures (including trailers and modular building components that canbe transported to emergency sites).

Referring to FIG. 9 a portable radiation detection system 900 caninclude a vehicle, for example truck 902, and a portable radiationdetection apparatus 1000 mounted on the vehicle. The portable detectionapparatus 1000 can be any suitable apparatus, and can include any of thefeatures of detection apparatus 100 described above.

Optionally, the vehicle 902 can include a radiation shielded chamber 904and the portable detection apparatus 1000 can be provided within theshielded chamber. In the example illustrated, the radiation shieldedchamber 904 is provided inside the cargo area of the truck 902, which isillustrated in a partially cut-away view. The walls 906 of the cargoarea can be shielded with any suitable material. The quantity ofshielding 908 may be relatively limited to help ensure that the weightof the shielding material 908 does not prevent operation of the truck902. The quantity of shielding 908 provided on the truck 902 isgenerally less than the quantity of shielding that can be providedaround a stationary scanning room.

Referring to FIG. 10 a method 1200 of using a portable detectionapparatus to measure the quantity of a beta-emitting radioactivematerial, for example ⁹⁰Sr/Y, disposed within a subject is illustrated.

Optionally, the method 1200 can include the step 1202 of transportingthe detection apparatus to a temporary testing location. The temporarytesting location can be any location where on-site radiation detectionis desired for a relatively short time period, and then the radiationdetection equipment is removed from the location (for example anemergency scene). The method can also include calibration steps tocalibrate the detector to the local environment.

Step 1204 includes positioning the portable detection apparatus adjacentthe torso of the subject.

The portable detection apparatus can be any type of portable detectionapparatus including those examples described herein. Optionally thedetection apparatus can include a first detector, configured to detect acombination of background radiation and a secondary radiation, and asecond detector, configured to detect the background radiation.

The method can also include the step 1206 of detecting a combination ofthe secondary radiation (for example Bremsstrahlung radiation) and thebackground radiation using the first detector and providing acorresponding a first output signal. At step 1208, the method 1200includes simultaneously detecting the background radiation using thesecond detector and providing a corresponding second output signal.Optionally, steps 1206 and 1208 can be conducted simultaneously.Alternatively, they can be conducted in series.

Step 1210 includes automatically calculating a resultant output valuebased on the first output signal and the second output signal. Step 1212includes comparing the resultant output value to a predetermined alarmthreshold value, and optionally generating an alarm output if theresultant output value exceeds the alarm threshold value at step 1214.

The method can include calculating the resultant output value bysubtracting the second output signal from the first output signal todetermine a first quantity of secondary radiation (e.g. Bremsstrahlungradiation) received by the detection apparatus.

Calculating the resultant output value further can include determiningthe quantity of radioactive material, for example ⁹⁰Sr/Y, containedwithin the patient based on the first quantity of Bremsstrahlungradiation.

Optionally, the resultant output value can include at least one of thequantity of Bremsstrahlung radiation and the quantity of ⁹⁰Sr/Ymaterial. For example, the portable detection apparatus can beconfigured to generate an alarm signal based on the calculated quantityof ⁹⁰Sr/Y disposed within a patient's lungs, or optionally baseddirectly on the measured Bremsstrahlung radiation levels, withoutrequiring the subsequent calculation of the ⁹⁰Sr/Y quantities or betaemission levels.

An experiment was conducted to study various aspects of the apparatusesand methods disclosed herein.

The study was directed to developing a portable ⁹⁰Sr detector suitablefor rapid bioassay in emergency situations. A method to detectbeta-emitters ⁹⁰Sr and its daughter ⁹⁰Y inside the human lung viabremsstrahlung radiation was also investigated using a 3″×3″ NaI(TI)crystal detector and a polyethylene encapsulated source to emulate humanlung tissue.

The results illustrate that this method may be a viable technique fordetecting ⁹⁰Sr with a minimum detectable activity (MDA) of 1.1×10⁴ Bqfor a realistic dual shielded detector system in a 0.25 μGy h⁻¹background field for a 100 scan shielded with 5 cm of lead. Theseresults are well below the recognized action level (i.e. a thresholdover which further medical treatment may be required) of 8.2×10⁴ Bq for⁹⁰Sr intake in the lungs. The experimental data was verified using MonteCarlo calculations (see for example FIGS. 14 and 15), including anestimate for internal bremsstrahlung, and an optimization of thedetector geometry was performed.

The study included the preparation of a ⁹⁰Sr source. As explained above,within a human lung, the beta particles emitted by the ⁹⁰Sr-⁹⁰Y decayand interact with the surrounding tissue to generate x-rays throughbremsstrahlung. These x-rays will then transport out of the body, wherethey may be detected. This detection indicates the presence of thebeta-emitter within the lung. In order to experimentally replicate thiseffect, a bremsstrahlung radiation source was devised and constructed.

The sensitivity requirement for in vivo lung counting technique forassessing internal contamination following an RN emergency was firstderived to guide the experimental design for source preparation. A dosethreshold of 0.1 Sv CED (committed effective dose) was chosen tocalculate the sensitivity required for the ⁹⁰Sr lung counting techniquesusing a dose calculation software GenmodPC. Similar same inputparameters for ⁹⁰Sr were used for calculation, including the mostcommonly available chemical form (titanate), ICRP default particlesolubility type (fast), f₁ (0.01) and inhalation dose coefficients(1.6×10⁻⁷ Sv Bq⁻¹) for the public (adults). This led to a daily lungburden of 8.5×10⁴−7.9×10⁴ Bq of ⁹⁰Sr within the first 5 days after aninhalation exposure of 0.1 Sv CED, with a lung burden of 8.2×10⁴ Bq inthe third day after exposure.

The experimental bremsstrahlung radiation source was made by evaporatinga ⁹⁰Sr standard solution (purchased from the National Institute ofStandard and Technology, US) within a recess inside a 2″ diameter and 2cm thick cylindrical polyethylene container. This was then covered withanother 2″ diameter and 2 cm cylindrical polyethylene slab and sealed.This source geometry was designed to emulate a practical ⁹⁰Sr inhalationscenario. Polyethylene was selected as a suitable tissue equivalentmaterial that substantially mimics human tissue (for example in bothZ-value and material density). Polyethylene gives a similarbremsstrahlung production probability compared to human tissue. The betasource activity was determined to be 112.1 kBq, excluding thecontribution of ⁹⁰Y.

An experimental ⁹⁰Sr detection apparatus was also constructed for testpurposes. The detection apparatus included a Bicron 3M3/3-X, which is astandard 3″×3″ NaI(TI) crystal optically coupled with a 3″ PMT. Thecrystal and

PMT were hermetically sealed within an aluminium case. This PMT wasmounted with a Saint-Gobain P-14 PMT base and operated with a highvoltage of +780 V. The output signal was then put through acharge-sensitive preamplifier and the resulting pulse height, whichcorresponds to detected particle energy, was recorded by the acquisitionsystem.

Detection of the ⁹⁰Sr-⁹⁰Y source was achieved through the detection ofbremsstrahlung radiation. When configured as a portable detector, it maybe advantageous to keep the overall size of the detection apparatus to aminimum while still retaining the capability to measure x-ray emissionfrom large surface areas (i.e. the torso of a patient). Thesespecifications made a NaI(TI) crystal a suitable candidate for testingas it is a dense, high-Z material capable of being produced as arelatively large single crystal, which may be preferred for gamma orx-ray detection. The final design of this detector may be small enoughand light enough to fit within an emergency mobile detection unit, suchas a truck or van, or may be hand-held or carryable by one or moreoperators.

Initial calibration of the experimental detector was performed usingweak sources of ⁶⁰Co (y: 1.17 and 1.33 MeV), ¹³⁷Cs (y: 662 keV), and¹³³Ba (y: 303 keV and 356 keV). As expected, the detected gamma energyscaled linearly with the PMT signal voltage. Recorded spectra are shownin FIG. 11. The FWHM of the signal peaks corresponding to these gammalines are approximately 60 keV for ⁶⁰Co, 40 keV for ¹³⁷Cs, and 30 keVfor ¹³³Ba.

Measurements were made with this detector setup for background andsource or secondary radiation for 2 hours each. Additional measurementswere later made for 30 minutes each, but with the inclusion of a 5 cmthick surrounding layer of Pb to reduce the ambient background. MonteCarlo calculations of the detector geometry were then compared to theexperimental data. These simulations helped in optimizing the detectorgeometry and identifying factors in the ⁹⁰Sr detection method discussed.The calculation was done using Geant4, a simulation toolkit based in theC++ programming language.

The inventors discovered that the region of interest (ROI) for theseexperiments was from about 0 keV to about 500 keV. This region wasselected based on the inventor's discovery that there is littlestatistical difference between the experimental source signal and theexperimental background signal beyond about 500 keV as thebremsstrahlung energy spectrum has a relatively low energy (similar tothat of the background radiation). See for example the spectra shown inFIG. 12.

For example, the measured spectra with and without the source can beseen in FIG. 12. A difference is noticeable between the combinedsecondary and background signal and the pure background signal, anintegrated total difference within the ROI was calculated to be about98,161±1,297. This error was calculated by summing the statisticalcounting errors of the source and background scans. This difference maybe significant when compared to the background count total ofapproximately 361,000 in the ROI. This may help confirm the capabilityof this technique to monitor inhaled ⁹⁰Sr even without conventional,bulky radiation shields.

The measured radiation intensity begins to drop off sharply below 120keV as this was the threshold of detection for the data acquisitionsystem used in this experiment. Since the bremsstrahlung process mainlygenerates lower energy x-rays, the counting statistics may not beoptimal as a result of the high threshold.

A Monte Carlo simulation was constructed with a simplified geometry. Thesimulation modelled the beta minus decay of the ⁹⁰Sr and ⁹⁰Y nuclei, thebremsstrahlung radiation subsequently generated within the polyethylenesource container, and the crystal scintillation as a result of thephoton energy loss in the crystal. The simulations were run with a totalof 6.726×10⁶ histories in order to simulate the approximate number ofdisintegrations in the 112.1 kBq source in the time span of 1 minute.

This simulation did not include the internal bremsstrahlung spectrum,which is the direct production of x-rays accompanying the beta decay.This phenomenon has a low energy x-ray spectrum similar to that ofexternal bremsstrahlung. The KUB theory describes the probability ofinternal bremsstrahlung interaction with a first-order approximation of_(nw) ^(α) where α is the fine structure constant (˜1/137) and w is theemitted photon energy in units of electron rest mass energy. Thisprobability is about ˜1% for 100 keV photons and decreases for higherenergies. This is in the same range as the probability of interactionfor external bremsstrahlung in the polyethylene container.

The experimental results of the unshielded experiment were comparedagainst the simulation results. This comparison showed good agreementbeyond 130 keV. A sharp drop-off shown in the measured data below 120keV was the result of the acquisition system threshold being defined at120 keV, meaning sampled pulse heights lower than those corresponding to120 keV x-rays were not recorded by the acquisition system.

To improve the source signal detection rate, a 5 cm thick layer of leadblocks were placed around the detector and source apparatus to reducethe acquisition time required for a scan. This structure simulates theshield described above. Measurements were made with this modifieddetector setup for background and source for 30 minutes each.

Referring to FIG. 13 with the presence of the shield, the backgroundsignal was attenuated significantly, providing a more prominentbremsstrahlung spectrum with an integrated total difference within theROI of 79,079±442. In the illustrated example, the background totalcount recorded in the ROI for this trial is approximately 17,300. Aswith the previous set of experimental data, the differential spectrumwas compared to the simulation results, which showed good agreement withthe experimental results combined with better statistics on thedifferential spectrum due to background reduction.

With the simulation verified against experimental data, it was foundthrough further simulations that there are factors in the detector setupwhich can be optimized.

One such factor is the NaI(TI) crystal thickness. Since the sourcedetection rate is dependent on the effective detector surface area andthe background rate is dependent on the detector volume, the inventorsdiscovered that it may be desirable for a detector to be as thin aspossible to help reduce the background signal. However, providing toothin a crystal may allow some x-rays to escape the detector volumewithout being detected. The simulation was run multiple times withdifferent crystal thicknesses, each with 2×10⁶ histories (number of Sr/Ydecays) for good statistics.

The efficiency was defined as:

$\begin{matrix}{ɛ = {\frac{n_{detected}}{N_{histories}}.}} & (1)\end{matrix}$

Referring to FIG. 14, a simulated efficiency curve shows littlesignificant efficiency gains for crystal thicknesses greater than 1″ andit was determined that a ½″ crystal could be used for the detection ofx-rays at the energies associated with this detection method.

Another factor found to affect the signal statistics was the thicknessof the aluminium housing surrounding the detector crystal. Since theenergy region of interest lies in the low energy range, the inventorsdiscovered that a thin layer of aluminum may be capable of attenuatingthe secondary radiation. Referring to FIG. 15, a simulation of thesignal below 50 keV appears to be attenuated as the aluminium housingthickness increases. Based on these results, the inventors believe thata 17.4% gain in the integrated signal above 30 keV may be achieved fromthinning the aluminum layer from 1.0 mm to 0.01 mm. The experimentaldetector geometry has an aluminium housing thickness of 0.5 mm. Thislayer also shifts the peak detectable x-ray energy. As shown in FIG. 15,the peak detection occurs at approximately 40 keV for an aluminiumthickness of 0.01 mm, but this moves closer to 60 keV at a thickness of1.0 mm.

For the characterisation of a portable detector, both the lower limit ofdetection (LLD) and the minimum detectable activity (MDA) may berelatively significant factors for the detection apparatus. It wasdetermined that a 5 minute scan may be one acceptable detection cycletime for a rapid bio-assay technique (i.e. on-site testing), and all theexperimental calculations were performed for an equivalent scan of 5minutes. Additionally, the background count rates were corrected for thedetector dead time previously calculated and all of the followingcalculations use a calculated detector efficiency of 0.4%, which wascalculated to be the total efficiency for an 3″×3″ NaI(TI) crystal inthis arrangement.

The LLD can be calculated as:

$\begin{matrix}{{L\; L\; D} = \frac{1.645\sqrt{R_{b}/t_{b}}}{ɛ\left( {{A/100}\mspace{14mu} {cm}^{2}} \right)}} & (2)\end{matrix}$

where R_(ν)is the background count rate (dead time corrected), t_(ν)isthe acquisition time of the background count, ε is the efficiency of thedetector, and A is the effective area of the detector. For theunshielded and shielded detector geometries, the LLD was determined tobe 401 Bq and 167 Bq, respectively. The MDA of this detector can becalculated as:

$\begin{matrix}{{M\; D\; A} = \frac{\left( {2.71/t} \right) + {4.65\sqrt{R_{b}/t}}}{ɛ\left( {{A/100}\mspace{14mu} {cm}^{2}} \right)}} & (3)\end{matrix}$

where t is the time of the scans. For the unshielded and shieldeddetectors, the MDA was calculated to be 1,132 Bq and 471 Bq,respectively. These results are well below the action level of 0.1 SvCED for ⁹⁰Sr inhalation.

Based on the experiments described above, the inventors have found thatthe bremsstrahlung x-ray emission from beta emitters ⁹⁰Sr-⁹⁰Y inside thelung may be successfully measured by an external NaI(TI) detectorarrangement. The experiment also shows that one example of a suitabledetector geometry includes a 3″×½″ Nal crystal, with a relatively thinlayer of aluminium surrounding the crystal. Also, the bremsstrahlungcount rate (background subtracted) for the unshielded detector was foundto be 10 counts s⁻¹ for a 112.1 kBq source, with a background count rateof 70 counts s⁻¹. The MDA for a 5 minute scan with this setup wasdetermined to be a source with an activity of 1,132. A Pb layer of 5 cmsurrounding the detector was found to help improve the bremsstrahlungnet count rate to 40 counts s⁻¹ for the same source, with a backgroundcount rate of 25 counts s⁻¹.

The non-limiting illustrative examples herein illustrate one or moreembodiments of a portable radiation detection apparatus and methodsuitable for detecting ⁹⁰Sr/Y. Other embodiments of a portable radiationdetection apparatus/method can be configured to be suitable fordetecting other radioactive materials, including, for example,beta-emitting radioactive materials.

While the subject is illustrated as a human patient 120, the portabledetection apparatus 100 can also be used to detect radiation in othertypes of subjects, including animals and plants that may have receivedinternal exposure to beta-emitting radioactive materials.

What has been described above has been intended to be illustrative ofthe invention and non-limiting and it will be understood by personsskilled in the art that other variants and modifications may be madewithout departing from the scope of the invention as defined in theclaims appended hereto.

1. A portable detection apparatus, comprising: a) a housing; b) a firstdetector within the housing for detecting ionizing radiation comprisingbackground radiation and secondary radiation from a subject; c) a seconddetector within the housing for the detecting the background radiation;d) a shield within the housing surrounding the first and seconddetectors and defining a shield aperture around the first and seconddetectors for radiation from the subject to enter the housing; e) aradiation blocking member substantially blocking at least a portion ofthe ionizing radiation entering the housing through the shield aperturefrom reaching the second detector, whereby radiation detected by thesecond detector comprises substantially only the background radiation;and f) a processor module connected to the first and second detectorsfor determining the amount of ionizing radiation detected by the firstdetector attributable to the secondary radiation.
 2. The apparatus ofclaim 1, wherein the housing defines a detection apparatus axis andbeing axially alignable with the subject, and the first detectorcomprises a first scintillator having an exposed first detection surfaceextending in a generally lateral direction and positionable opposite thesubject, and the second detector comprising a second scintillator havingan second detection surface extending in the generally lateraldirection.
 3. The apparatus of claim 1, wherein the radiation blockingmember covers substantially all of the second detection face, wherebythe secondary radiation is substantially prevented from reaching thesecond detection face and optionally wherein the shield apparatuslaterally surrounds the first scintillator and the second scintillatorand the shield aperture is registered with the first detection surfaceand the second detection surface.
 4. (canceled)
 5. The apparatus ofclaim 1, wherein the first scintillator produces a first light whenexcited by the ionizing radiation and the second scintillator produces asecond light when excited by the ionizing radiation and furthercomprising a photosensor positioned adjacent the first and secondscintillators to receive the first light and generate a correspondingfirst output signal, and to receive the second light and generate acorresponding second output signal; and optionally wherein the processormodule is operably linked to the photosensor and is operable todetermine the amount of ionizing radiation detected by the firstdetector attributable to the secondary radiation by comparing the secondoutput signal with the first output signal; and optionally wherein theprocessor module is operable to determine a quantity of the radioactivematerial contained in the subject based on the amount of ionizingradiation detected by the first detector attributable to the secondaryradiation measured by the detection apparatus and optionally wherein theprocessor module is operable to compare at least one of the amount ofionizing radiation detected by the first detector attributable to thesecondary radiation and the quantity of radioactive material containedin the subject to a predetermined alarm threshold value and generate analarm signal if the at least one of the amount of ionizing radiationdetected by the first detector attributable to the secondary radiationand the quantity of radioactive material contained in the subjectexceeds the alarm threshold value and optionally wherein the photosensorcomprise a first photomultiplier tube to receive the first light andgenerate the first output signal and a second photomultiplier tube toreceive the second light and generate the second output signal. 6.(canceled)
 7. (canceled)
 8. (canceled)
 9. (canceled)
 10. The apparatusof claim 1, wherein the radiation blocking member has a thicknessbetween about 0.05 mm and about 5 mm; and optionally wherein theradiation blocking member comprises a plate member; and optionallywherein the plate member comprises at least one of copper, tin, andaluminum or a combination thereof; and optionally wherein the radiationblocking member allows transmission of the background radiation therethrough, whereby the background radiation can reach the second detector.11. (canceled)
 12. (canceled)
 13. (canceled)
 14. The apparatus of claim1, wherein the shield comprises a) a first shielding layer formed from afirst material, b) a second shielding layer formed from a secondmaterial and disposed laterally inboard of the first shielding layer;and c) a third shielding layer disposed laterally inboard of the secondshielding layer; and optionally wherein the first shielding layer has afirst lateral width, the second shielding layer has a second lateralwidth and the third shielding layer has a third lateral width, the firstlateral width being greater than the both the second and third lateralwidths; and optionally wherein the first shielding layer is formed fromlead or tungsten, and the first lateral width is between about 2.5 mmand 125 mm; and optionally wherein the second shielding layer is formedfrom tin, and the second lateral width is between about 0.25 mm andabout 25 mm; and optionally wherein the third shielding layer is formedfrom copper, and the third lateral width is between about 0.25 mm andabout 25 mm.
 15. (canceled)
 16. (canceled)
 17. (canceled)
 18. (canceled)19. The apparatus of claim 1, wherein the first and second scintillatorscomprise first and second detection crystals, respectively, andoptionally wherein the first scintillator has an overall surface areaand the first detection surface has a detection surface area, and thedetection surface area is between about 25% and about 45% of the overallsurface area; and optionally wherein the first scintillator has a firstthickness in the axial direction of less than about 25 mm; andoptionally wherein the first and second detection crystals compriseNaI(TI) crystals; and optionally wherein the second scintillator isgenerally identical to the first scintillator.
 20. (canceled) 21.(canceled)
 22. (canceled)
 23. (canceled)
 24. The apparatus of claim 1,wherein time elapsed between exposure of the detection apparatus to thesource of the secondary radiation and obtaining the resultant outputsignal defines a detection cycle time, and the detection cycle time isless than about 10 minutes; and optionally wherein the detection cycletime is less than about 2 minutes.
 25. (canceled)
 26. The apparatus ofclaim 1, wherein the detection apparatus is a mountable on a vehicle.27. The apparatus of claim 1, wherein radioactive material within thesubject emits beta radiation and the secondary radiation isbremsstrahlung radiation produced by an interaction between the betaradiation from the radioactive material and the subject.
 28. Theapparatus of claim 1, wherein the detection apparatus is configured tomeasure photons having an energy that is less than about 500 keV; andoptionally wherein the detection apparatus is configured to measurephotons having an energy that is greater than about 30 keV. 29.(canceled)
 30. The apparatus of claim 1 wherein the detection apparatushas an operating sensitivity capable of detecting an activity of atleast about 460 Bq within the subject using a 5 minute scan.
 31. Aportable radiation detection system comprising: a) a vehicle; and b) aportable radiation detection apparatus according to any one of claims 1to 30 mounted on and transportable with the vehicle; and optionallywherein the vehicle comprises a radiation shielded chamber, and thefirst and second detectors are provided within the shielded chamber. 32.(canceled)
 33. A method of measuring the quantity of a beta-emittingradioactive material within a subject using a portable detectionapparatus, the method comprising: a) positioning the portable detectionapparatus adjacent the subject, the portable detection apparatuscomprising a first detector, configured to detect ionizing radiationcomprising background radiation and secondary radiation, and a seconddetector configured to detect ionizing radiation; b) detecting acombination of the secondary radiation and the background radiationusing the first detector and providing a corresponding a first outputsignal; c) simultaneously detecting the background radiation using thesecond detector and providing a corresponding second output signal; andd) automatically calculating a resultant output value based on at leastthe first output signal and the second output signal.
 34. The method ofclaim 33, further comprising comparing the resultant output value to apredetermined alarm threshold value, and generating an alarm output ifthe resultant output value exceeds the alarm threshold value.
 35. Themethod of claim 33, wherein calculating the resultant output valuecomprises comparing subtracting the second output signal from the firstoutput signal to determine a first quantity of secondary radiationreceived by the detection apparatus.
 36. The method of claim 33, whereincalculating the resultant output value further comprises determining asecond quantity of radioactive material contained within the subjectbased on the first quantity of secondary radiation.
 37. The method ofclaim 33, wherein the resultant output value comprises at least one ofthe first quantity of secondary radiation and the second quantity ofradioactive material.
 38. The method of claim 33, further comprisingtransporting the portable detection apparatus to a temporary testinglocation.
 39. The method of claim 33, further comprising positioning aradiation blocking member between the second detector and the subject toinhibit the secondary radiation from reaching the second detector.